CRH: A system, the abbreviation of high speed railway, it means a road which do not represent trains running on railway. For example, Xicheng CRH, Wuhan Guangzhou CRH and Beijing-Shanghai CRH.
CRH system covers orbit system, rolling stock system, signal system, power supply system and dispatching system, and EMU is only one part of them.
EMU: The rolling stock, that is, we often take the G-train or D-train are EMU trains. It is composed of 1 or 2 with their own power and some trains without power to form a fixed, non changing train group.
According to the dynamic configuration, it can be divided into power EMU (power source in multiple railway carriages) and dynamic concentrated EMU (powered by the first railway carriage and the last carriage)
But In our daily lift, "Gaotie" usually refers to "G-train", "Dongche" usually means "D-train".
The first differentia between G-train and D-train is the ticket price:
The ticket price for G-train is about 0.48RMB/km.
The ticket price for D-train is about 0.31RMB/km
The second differentia is running speed:
Until now, the high speed train lines which designed running speed is 350km/hour are Beijing Tianjin Intercity, Beijing-Shanghai CRH, Shanghai Hangzhou CRH, ZhengXi CRH and Wuhan Guangzhou CRH, and only the "Fuxing" bullet train belongs to Beijing-Shanghai CRH can achieve 350km/h running speed.
The third differentia is railway line:
G-train can only run on the new CRH railway line.
D-train can run both on ordinary railway line and new CRH railway line.
G-train is the highest grade in the train diagram, so D-train shall dodge G-train when meeting.
The last difference is train model:
G-train adopts CRH2C、CRH3、CRH380 series bullet trains.
D-train adopts CRH1、CRH2（besides 2C) 、CRH5 series bullet trains.
As usual , the internal unit of G-train is better and advanced than D-train.